Public interest law refers to legal practices undertaken to help poor, marginalized, or under-represented people, or to effect change in social policies in the public interest, on 'not for profit' terms (pro bono publico), often in the fields of civil rights, civil liberties, religious liberty, human rights, women's rights, consumer rights, environmental protection, and so on.

In a celebrated 1905 speech, Louis Brandeis decried the legal profession, complaining that "able lawyers have to a large extent allowed themselves to become adjuncts of great corporations and have neglected their obligation to use their powers for the protection of the people."

In the tradition thus exemplified, a common ethic for public-interest lawyers in a growing number of countries remains "fighting for the little guy".

At the end of the communist period in the early 1990s, the national legal systems of Central and Eastern Europe were still in a formative stage. The most important source of legal authority for the new human rights groups came from outside the region: the Council of Europe, with its European Convention on Human Rights, and the European Court of Human Rights.

Over time, in the mid-1990s, U.S. experiences became more relevant. The Council of Europe's prerequisite that lawyers use their own country's courts first to seek legal remedies before turning to the European bodies gradually became more than a pro forma exercise, and civil society organizations began to make more effective use of domestic means of adjudication. But by the time local activists were ready to consider the utility of impact litigation, test cases, and other tactics familiar from the U.S. experience, they already understood that their ultimate tactical weapon in any piece of litigation was to use the threat or reality of a supportive decision at the European Court of Human Rights. With this background in mind, it made more sense for the promoters of public interest law in Central and Eastern Europe to talk about "strategic litigation" than about public interest litigation. Using the instrumentality of the European Court of Human Rights effectively required a strategic approach. Not all human rights cases were likely to receive a favorable ruling; a negative ruling could produce more damage to the human rights cause than no ruling at all. The European Court had a rich case law that could provide clues to how a future case might be decided, and there were procedural aspects, such as the requirement to exhaust domestic remedies, to consider.

The core lesson from the U.S. experience for local activists was how courts could be used effectively as a tool for civil society engagement in governance.

The changes to the Italian electoral law from 2014 to 2017 were both "caused by actions born from the bottom (...) the result of a methodical, studied and concerted action. It has been featured by university professors, constitutional and electoral law-makers, parliamentarians and other elected representatives (...), representatives of civil society and ordinary citizens. Their names are, as voters, in more than twenty introductory pleadings (quotations or appeals)", all of them brought pro bono.

Public interest law (公益法) is an accepted term in China, where the basic institutions supporting the rule of law are still extremely nascent. China does not have a common-law system in which lawyers are expected to play a key role in "making law." Nevertheless, a small but effective community of lawyers has gained acceptance of public interest litigation as a legitimate means of resolving social issues and contributing to a harmonious society, and non-governmental actors have significantly improved the enforcement of rights for migrant workers, women, children and those suffering from environmental degradation, among others. For example, public interest lawyers in China have filed lawsuits in court successfully challenging workplace sexual harassment and the involuntary confinement of healthy people to mental hospitals.